During the summer, when storage operators are typically injecting natural gas into storage facilities to build up inventories before the winter months, natural gas inventories in Southern California have remained nearly flat. Underground natural gas storage wells at the Southern California Gas Company (SoCalGas) Aliso Canyon facility, by far the largest storage field in the region, are undergoing testing, following a leak that was detected in late October 2015 and stopped in February 2016. Approval from regulators is required before operators can begin to inject natural gas into this storage field.
Aliso Canyon accounts for 86 billion ft3 of SoCalGas's total capacity of 135 billion ft3. After the leak, the California Public Utilities Commission (CPUC) ordered that Aliso Canyon inventory levels be reduced to 15 billion ft3. Other SoCalGas storage fields, with a combined capacity of 49 billion ft3, are nearly full. The inventory levels in these fields are estimated at 46 billion ft3, or 93% of capacity, based on data provided by SoCalGas.
Aliso Canyon is connected to the Los Angeles Basin's lower pressure local natural gas transmission system, sometimes referred to as the L.A. Loop. Prior to the leak, Aliso Canyon could provide up to 1.9 billion ft3/d, a specification known as sendout capacity. Only one other SoCalGas storage field (Playa del Ray) is connected to this system, but it has a much lower sendout capacity of 0.4 billion ft3/d. Two other SoCalGas storage fields have a combined sendout capacity of 1.4 billion ft3/d, but are farther away or not well connected to the L.A. Loop.
The California Department of Conservation's Division of Oil, Gas, and Geothermal Resources ordered testing of each of the 114 wells at Aliso Canyon before injection may resume. As of 8 August, 17 wells have passed all tests. The remaining wells are being tested or have test results pending. During March and April, wells were tested for temperature and noise, as any leaking gas would create noise and be detectable by changes in temperature in the well casing.
During the leak, the exact emissions rate and cumulative leakage were unknown, and changes in inventory levels only reflected net changes in natural gas sendouts and receipts. In late May, SoCalGas completed the physical measurement of its gas inventory and provided an estimate of the leaked volume. SoCalGas estimated that 4.62 billion ft3 leaked over the span of 112 days, an amount equivalent to 84 200 t of methane. On 20 June, SoCalGas subtracted 4.62 billion ft3 of natural gas from its total inventory.
Adapted from press release by Rosalie Starling
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